It has been shown that SPECT reconstruction when using cone-beam or multifocal (cardiofocal) collimators is subject to “cone-beam” type artifacts. These artifacts are easily recognized using a Defrise phantom, which consist of a series of hot and cold plates arranged along the axis of rotation. They occur because in local regions away from the central mid-plane, neither the Orlov nor the Tuy sampling completeness criteria are satisfied for either circular or non-circular camera orbits in a plane perpendicular to the axis of rotation. As a consequence, spatial frequency components around the axial direction are not well determined. This may cause degradation of spatial resolution in the axial direction as well as some spatial distortions. In Defrise phantom images, such artifacts are readily recognized; however, with clinical cardiac images, artifacts may be hard to recognize, and their presence reduces the accuracy of image interpretation.
Furthermore, statistically based image reconstruction such as MLEM or OSEM may be somewhat more tolerant to sampling incompleteness (when using cone-beam or multifocal collimation) than FBP. Still, however, there is significant degradation from incomplete sampling.